The crotch grab is a reoccurring event in the later games of the Metal Gear series, usually played for humor. The act involves a person clutching the crotch of another, which has been used to verify gender, identity, or to knock a male unconscious when done with sufficient force.
Metal Gear Solid 2: Sons of Liberty
In Metal Gear Solid 2: Sons of Liberty, President Johnson executes a crotch grab on Raiden. He later exclaims, "You're... a man!?", suggesting that he mistook him for a woman due to Raiden's androgynous appearance. According to the game's script, Johnson had actually mistaken Raiden for Olga Gurlukovich. Despite the humorous and seemingly unnecessary nature of the scene, it actually foreshadows Olga's allegiance to the Patriots, as Johnson believes she has been sent to kill him for cooperating with Solidus Snake.
In its expansion game Substance, one of the alternate missions, depicting a murder investigation relating to Raiden's murder, had Raiden clutching his groin, implying his murderer is James Johnson, as well as referring to his aforementioned action above.
Metal Gear Solid 3: Snake Eater
Naked Snake twice receives a crotch grab from Colonel Volgin in Metal Gear Solid 3: Snake Eater. Suspicious of Naked Snake, who was disguised as his lover Major Raikov, Volgin performed the grab in order to confirm his identity. Volgin also regularly does this with Raikov. Raikov will also sometimes perform one on Snake, if he wears the Raikov Mask and scientist disguise, after remarking "Hey...!" Snake, while disguised as Raikov, will also grab soldiers' genitalia while saluting.
In Subsistence, two more variations of the crotch grab are observed. In Metal Gear Online, Raikov, as the leader of the GRU, is able to perform the crotch grab as a special, 1-hit knockout CQC attack. The other instance is during the Secret Theater short, Snake Eraser. Raiden from the future, in his attempt to assassinate Big Boss, has his crotch grabbed by Volgin inside a jail cell, who believes him to be Raikov due to the resemblance between the two. In addition, although technically not a crotch grab, a similar attack can be utilized by the player by going into first-person mode and then punching or simply kicking a soldier directly in the crotch. This could easily be done while disguised as Major Raikov, due to the soldiers not suspecting that "Raikov" was being impersonated.
Metal Gear Solid 4: Guns of the Patriots
The crotch grab is featured in Metal Gear Solid 4: Guns of the Patriots as a CQC move, which Old Snake can use to knock out his enemies instantly while he is holding them up. The move is, however, totally ineffective on Haven Troopers, since they are composed solely of women. Any attempt to perform a crotch grab on a Haven Trooper will result in you groping them and them saying "Pervert!" or "You idiot!" retaliation commencement of the Alert Phase, unless you're wearing Young snake face camo. This was not implemented into Metal Gear Online.
During the Middle East mission, while utilizing OctoCamo on a statue podium, Old Snake will grab the crotch of the statue and pose. Perform this enough times and he will snap the genitals off.